The two adrenal glands, which derive their name from their location in the body (“ad” means near; “renal” means kidney), are key players in your body’s response to stress. Situated on top of the kidneys, these pyramid-shaped organs, the size of walnuts, are actually two endocrine glands in one: an inner medulla, which orchestrates your short-term stress response, and an outer cortex, which mediates your adaptation to chronic stress.

The primary hormone of the medulla is epinephrine, also called adrenalin. This powerful, short-acting hormone is secreted in response to the four E’s: exercise, excitement, embarrassment, and emergency. The flood of adrenaline that is unleashed in these situations causes a number of dramatic physical changes throughout your body: your heart beats more rapidly and forcefully; your pupils dilate; and blood is shunted toward your skeletal muscles, heart, and brain. Glycogen in your liver is converted into glucose to be used for quick energy. You may break out into a cold sweat and begin breathing more rapidly. In short, your body is mobilized for action. This is why adrenaline is known as the “fight or flight” hormone.

Adrenaline’s effects are dramatic and unmistakable, but because this hormone does not linger in your body, its effects are also relatively short-lived. On the other hand, cortisol, the stress hormone produced by the outer cortex, has more prolonged effects on your body. If adrenaline is like the whip that drives the horse faster and faster, cortisol is like the rider’s boot, digging into the flank, keeping the horse going even when it’s ready to quit.

The primary function of cortisol is to promote gluconeogenesis, the conversion of fats and proteins to sugar (glucose). Gluconeogenesis is an essential component of your body’s adaptation to chronic stress, ensuring that your vital organs, especially your brain, heart, and skeletal muscles, have enough energy to meet the increasing workload. In addition, cortisol assists adrenaline in stimulating the cardiovascular system, increasing the heart rate and pumping capacity and temporarily raising blood pressure. Cortisol also decreases inflammation, which is why this hormone and its counterfeit derivatives have been used to treat inflammatory conditions, such as allergies, asthma, arthritis, and skin disorders.

Due to its metabolic effects, high levels of cortisol can be extremely damaging. People with chronically elevated levels of cortisol may have high blood sugar and insulin levels and high blood pressure; they may gain weight, especially around the abdomen; and they have a greater risk of heart disease. However, just because high levels of cortisol are harmful doesn’t mean that low levels are healthy. As with all hormones, balance is the key.